-the world as I see it
If you’ve ever been to Lisbon, you would most definitely have spent quite a bit of your time downtown in the Baixa area – the neighbourhood with historical buildings, narrow streets and alleyways exuding an old world grungy charm. This post tells you a little something about the buildings in the Baixa area and sheds some light on why they were built that way.
The buildings in the Baixa area are aligned in quarters with shared walls. These buildings were built in the aftermath of the massive earthquake and the ensuing tsunami that rocked Lisbon in 1755 . The tsunami wiped out the entire downtown area, which was why the king commissioned the then Prime Minister, Marques de Pombal, to rebuild the place keeping two things in mind – the city had to get back on its feet quickly and the new constructions had to possess seismic resistance. Pombal and his team of engineers came up with a plan for these new seismically resistant buildings (which came to be known as Pombalino buildings) and which are now found all over the Baixa area. Typically, the only openings in the ground floor of these buildings are doors while the first floor mostly has doors with balconies. In the floors above, openings are in the form of windows only. There are roof openings as well, which could be doors or windows.
Since the area on which the buildings are built lies very close to the river Tagus, the buildings were given a wooden pile foundation extending through the layer of alluvial soil. Between the ground floor and the first floor, a system of arches or vaults, together with solid walls and columns was used. This system blocked off any possible spread of fire to the rest of the superstructure. The storeys above were composed of timber frames and masonry walls. The three-dimensional timber frame structure of the building is like a cage which is why it gets its name ‘gaiola.’ The gaiola forms the major load resistance mechanism.
When originally built, the ground floor of the buildings was meant for commercial use and the upper floors were supposed to be residential. However a lot of the buildings have now been occupied by banks,companies and hostels. The hostel ‘Rossio’ and the ‘Good Morning’ hostel are Pombalino buildings and it is even possible to see the exposed timber framework walls in their foyers.
The Pombalino buildings are an integral part of Lisbon’s architectural heritage and hence need to be maintained and preserved. They are also one of the foremost examples of seismically resistant earthquake constructions in Europe. Unfortunately many of these buildings have fallen into disrepair. Many researchers across Portugal are studying the Pombalino buildings and their components in an effort to design appropriate and non-invasive strengthening and retrofitting interventions for these historic structures.
I tried to restrict myself from being too technical in this post. So if you are interested in knowing more about this construction system from a structural engineering point of view, you can read the entry in the World Housing Encyclopedia.